Editing Bird vocalization (section)

==Function==
[[File:Corvus coronoides -Victoria, Australia-8.jpg|thumb|upright|The Western [[Australian raven]] (''Corvus coronoides'', ssp. ''perplexus'') makes a slow, high-pitched ''ah-ah-aaaah'' sound.<ref name="AM">{{cite web|url=http://www.amonline.net.au/factSheets/crows_ravens.htm|author=Australian Museum Online|title=Crows and Ravens| access-date = 12 August 2007| archive-url= https://web.archive.org/web/20070901222040/http://www.amonline.net.au/factSheets/crows_ravens.htm| archive-date= 1 September 2007 | url-status= live}}</ref> {{audio|An audio recording of an Australian Raven (Corvus coronoides).wav|Australian raven territorial call}}]]

One of the two main functions of bird song is mate attraction.<ref name="Catchpole">{{cite book |last1=Catchpole |first1=C. |last2=Slater |first2=P.J.B |title=Bird Song: Biological Themes and Variation |date=2008 |publisher=Cambridge University Press |isbn=978-0-521-87242-3}}</ref> Scientists hypothesize that bird song evolved through [[sexual selection]], and experiments suggest that the quality of bird song may be a good indicator of fitness.<ref name="springerlink.com">{{cite journal|author1=Read, A. W. |author2=D. M. Weary |name-list-style=amp|year=1990|title=Sexual selection and the evolution of bird song: A test of the Hamilton-Zuk hypothesis|journal=Behavioral Ecology and Sociobiology|volume=26|issue=1|pages=47–56|doi=10.1007/BF00174024|bibcode=1990BEcoS..26...47R |s2cid=25177326 }}</ref><ref name="Mikula">{{cite journal|author1=Mikula, P.|author2=Valcu, M.|author3=Brumm, H.|author4=Bulla, M.|author5=Forstmeier, W.|author6= Petrusková, T.|author7=Kempenaers, B. |author8= Albrecht, T.|name-list-style=amp|year=2021|title= A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection|journal=Ecology Letters|volume=24|issue=3|pages=477–486|doi= 10.1111/ele.13662|pmid=33314573|doi-access=free|bibcode=2021EcolL..24..477M }}</ref> Experiments also suggest that parasites and diseases may directly affect song characteristics such as song rate, which thereby act as reliable indicators of health.<ref>{{cite journal|author1=Garamszegi, L. Z.|author2=A. P. Møller|author3=János Török|author4=Gábor Michl|author5=Péter Péczely|author6=Murielle Richard|year=2004|title=Immune challenge mediates vocal communication in a passerine bird: an experiment|journal=Behavioral Ecology|volume=15|issue=1|pages=148–157|doi=10.1093/beheco/arg108|url=http://real.mtak.hu/4298/1/1104781.pdf|doi-access=free|access-date=2019-04-10|archive-date=2021-04-15|archive-url=https://web.archive.org/web/20210415062234/http://real.mtak.hu/4298/1/1104781.pdf|url-status=live}}</ref><ref>{{cite journal|author1=Redpath, S. M. |author2=Bridget M Appleby |author3=Steve J Petty |year= 2000|title=Do male hoots betray parasite loads in Tawny Owls?|journal=Journal of Avian Biology|volume=31|issue=4|pages=457–462|doi=10.1034/j.1600-048X.2000.310404.x}}</ref> The song repertoire also appears to indicate fitness in some species.<ref>{{cite journal|author1=Reid, J. M.|author2=Peter Arcese|author3=Alice L. E. V. Cassidy|author4=Sara M. Hiebert|author5=James N. M. Smith|author6=Philip K. Stoddard|author7=Amy B. Marr|author8=Lukas F. Keller|name-list-style=amp|year=2005|title=Fitness Correlates of Song Repertoire Size in Free-Living Song Sparrows (''Melospiza melodia'')|journal=The American Naturalist|volume=165|pages=299–310|doi=10.1086/428299|pmid=15729661|issue=3|bibcode=2005ANat..165..299R |s2cid=12547933|url=http://www.zora.uzh.ch/3239/2/05_Reid_etal_AmNatV.pdf}}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name = "Møller 2005 223-237" >{{cite journal |author1=Møller AP |author2=J. Erritzøe |author3=L. Z. Garamszegi |year=2005 |title=Covariation between brain size and immunity in birds: implications for brain size evolution |journal=Journal of Evolutionary Biology |volume=18 |issue=1 |pages=223–237 |doi=10.1111/j.1420-9101.2004.00805.x |url=http://www.birdresearch.dk/unilang/articles/Molleretal_2005_JEBb.pdf |pmid=15669979 |citeseerx=10.1.1.585.3938 |s2cid=21763448 |access-date=2008-03-10 |archive-date=2016-04-12 |archive-url=https://web.archive.org/web/20160412045133/http://www.birdresearch.dk/unilang/articles/Molleretal_2005_JEBb.pdf |url-status=live }}</ref> The ability of male birds to hold and advertise [[territory (animal)|territories]] using song also demonstrates their fitness. Therefore, a female bird may select males based on the quality of their songs and the size of their song repertoire.

The second principal function of bird song is territory defense.<ref name="Catchpole"/> Territorial birds will interact with each other using song to negotiate territory boundaries. Since song may be a reliable indicator of quality, individuals may be able to discern the quality of rivals and prevent an energetically costly fight.<ref name="springerlink.com"/> In birds with song repertoires, individuals may share the same song type and use these song types for more complex communication.<ref name="Searcy">{{cite journal |last1=Searcy |first1=W. A. |last2=Beecher |first2=M.D. |title=Song as an aggressive signal in songbirds |journal=Animal Behaviour |date=2009 |volume=78 |issue=6 |pages=1281–1292|doi=10.1016/j.anbehav.2009.08.011 |s2cid=30360474 }}</ref> Some birds will respond to a shared song type with a song-type match (i.e. with the same song type).<ref>{{cite journal |last1=Falls |first1=J. B. |last2=Krebs |first2=J. R. |last3=McGregor |first3=P.K. |title=Song matching in the great tit (Parus major) the effect of similarity and familiarity. |journal=Animal Behaviour |date=1982 |volume=30 |issue=4 |pages=997–1009|doi=10.1016/S0003-3472(82)80188-7 |s2cid=53189625 }}</ref> This may be an aggressive signal; however, results are mixed.<ref name="Searcy"/> Birds may also interact using repertoire-matches, wherein a bird responds with a song type that is in its rival's repertoire but is not the song that it is currently singing.<ref name="ReferenceA">{{cite journal |last1=Beecher |first1=M.D. |last2=Stoddard |first2=P.K. |last3=Cambell |first3=E.S. |last4=Horning |first4=C.L. |s2cid=26372750 |title=Repertoire matching between neighbouring song sparrows. |journal=Animal Behaviour |date=1996 |volume=51 |issue=4 |pages=917–923|doi=10.1006/anbe.1996.0095 }}</ref> This may be a less aggressive act than song-type matching.<ref name="ReferenceA"/> Song complexity is also linked to male territorial defense, with more complex songs being perceived as a greater territorial threat.<ref>{{cite journal |author1= Hill, S. D. |author2= Brunton, D. H. | author3= Anderson, M. A. | author4= Weihong, J. | year=2018| title= Fighting talk: complex song elicits more aggressive responses in a vocally complex songbird| journal=Ibis| volume=160| pages=257–268| doi=10.1111/ibi.12542| issue=2| doi-access=free}}</ref>

Birds communicate alarm through vocalizations and movements that are specific to the threat, and bird alarms can be understood by other animal species, including other birds, in order to identify and protect against the specific threat.<ref>{{cite web |year=2008 |title=A Bird's World: Speaking in a Bird's Language |publisher=Museum of Science, Boston |url=http://www.mos.org/educators/field_trip_resources/field_trip_activities/exhibits%26d%3D215 |archive-date=2012-03-22 |url-status=dead |access-date=2023-02-13 |archive-url=https://web.archive.org/web/20120322075102/http://www.mos.org/educators/field_trip_resources/field_trip_activities/exhibits%26d%3D215 }}</ref> [[Mobbing behaviour|Mobbing]] calls are used to recruit individuals in an area where an owl or other predator may be present. These calls are characterized by wide frequency spectra, sharp onset and termination, and repetitiveness that are common across species and are believed to be helpful to other potential "mobbers" by being easy to locate. The alarm calls of most species, on the other hand, are characteristically high-pitched, making the caller difficult to locate.<ref>{{cite journal |author=Marler, P. |year=1955 |title=Characteristics of some animal calls |journal=Nature |volume=176 |issue=4470 |pages=6–8 |doi=10.1038/176006a0|bibcode=1955Natur.176....6M |s2cid=4199385 }}</ref>
Communication through bird calls can be between individuals of the same species or even across species. For example, the [[Japanese tit]] will respond to the recruitment call of the [[willow tit]] as long as it follows the Japanese tit alert call in the correct alert+recruitment order.<ref name="Mason">{{cite journal |last1=Mason |first1=Betsy |title=Do birds have language? It depends on how you define it. |journal=Knowable Magazine |publisher=Annual Reviews |date=15 February 2022 |doi-access=free |doi=10.1146/knowable-021522-1 |url=https://knowablemagazine.org/article/mind/2022/do-birds-have-language |access-date=22 February 2022 |archive-date=21 February 2022 |archive-url=https://web.archive.org/web/20220221180632/https://knowablemagazine.org/article/mind/2022/do-birds-have-language |url-status=live }}</ref>

Individual birds may be sensitive enough to identify each other through their calls. Many birds that nest in colonies can locate their chicks using their calls.<ref>{{cite journal|name-list-style=amp|author1=Lengagne, T.|author2=J. Lauga|author3=T. Aubin|year=2001|title=Intra-syllabic acoustic signatures used by the King Penguin in parent-chick recognition: an experimental approach|journal=The Journal of Experimental Biology|volume=204|pages=663–672|url=http://jeb.biologists.org/cgi/reprint/204/4/663.pdf|pmid=11171348|issue=Pt 4|doi=10.1242/jeb.204.4.663|bibcode=2001JExpB.204..663L |access-date=2007-05-13|archive-date=2007-09-30|archive-url=https://web.archive.org/web/20070930043626/http://jeb.biologists.org/cgi/reprint/204/4/663.pdf|url-status=live}}</ref> Calls are sometimes distinctive enough for individual identification even by human researchers in ecological studies.<ref>{{cite journal|first1=Wayne |last1=Delport |first2=Alan C. |last2=Kemp |first3=J. Willem H. |last3=Ferguson |year=2002|title=Vocal identification of individual African Wood Owls ''Strix woodfordii'': a technique to monitor long-term adult turnover and residency |journal=Ibis |volume=144 |issue=1 |pages=30–39 |doi=10.1046/j.0019-1019.2001.00019.x}}</ref>

[[File:Poecile atricapillus - Black-capped Chickadee - XC70185.ogg|right|thumb| Call of [[black-capped chickadee]] (note the call and response with a second more distant chickadee)]]
Over 400 bird species engage in duet calls.<ref>{{Cite journal |last=Hall |first=Michelle, L. |date=2009 |title=Chapter 3 A Review of Vocal Duetting in Birds |url=https://doi.org/10.1016/S0065-3454(09)40003-2 |journal=Advances in the Study of Behavior |volume=40 |pages=67–121|doi=10.1016/S0065-3454(09)40003-2 |isbn=978-0-12-374475-3 |url-access=subscription }}</ref> In some cases, the duets are so perfectly timed as to appear almost as one call. This kind of calling is termed antiphonal duetting.<ref>{{cite journal|author=Thorpe, W. H.|journal= Nature|volume=197|pages=774–776|date=23 February 1963|doi=10.1038/197774a0|bibcode= 1963Natur.197..774T|title=Antiphonal Singing in Birds as Evidence for Avian Auditory Reaction Time|issue=4869|s2cid= 30542781}}</ref> Such duetting is noted in a wide range of families including quails,<ref>{{cite journal|author=Stokes, A. W.|author2=H. W. Williams|year=1968|title=Antiphonal calling in quail|journal=Auk|volume=85|issue=1|pages=83–89|url=http://sora.unm.edu/sites/default/files/journals/auk/v085n01/p0083-p0089.pdf|doi=10.2307/4083626|jstor=4083626|access-date=2013-09-20|archive-date=2014-04-29|archive-url=https://web.archive.org/web/20140429184104/http://sora.unm.edu/sites/default/files/journals/auk/v085n01/p0083-p0089.pdf|url-status=live}}</ref> [[bushshrike]]s,<ref>{{cite book |last=Harris |first=Tony |author2=Franklin, Kim |title=Shrikes and Bush-Shrikes |publisher=Princeton University Press |pages=257–260 |isbn=978-0-691-07036-0 |year=2000}}</ref> [[old world babbler|babbler]]s such as the [[scimitar babbler]]s, and some owls<ref>{{cite journal |author=Osmaston, B. B. |year= 1941 |title= "Duetting" in birds|journal=Ibis| volume=5|pages=310–311|doi=10.1111/j.1474-919X.1941.tb00620.x|issue=2}}</ref> and parrots.<ref>{{cite journal |author=Power, D. M.|year=1966|title= Antiphonal duetting and evidence for auditory reaction time in the Orange-chinned Parakeet|journal= Auk|volume= 83|issue=2|pages= 314–319|doi=10.2307/4083033|jstor=4083033}}</ref> In territorial songbirds, birds are more likely to [[wikt:countersing|countersing]] when they have been aroused by simulated intrusion into their territory.<ref>{{cite journal |title=Countersinging as a signal of aggression in a territorial songbird |author=Hyman, Jeremy |journal=Animal Behaviour |year=2003 |volume=65 |pages=1179–1185 |doi=10.1006/anbe.2003.2175 |url=http://www.biology.duke.edu/nowicki/pdf/Hyman2003.pdf |issue=6 |s2cid=38239656 |access-date=2008-09-10 |archive-date=2012-03-08 |archive-url=https://web.archive.org/web/20120308160737/http://www.biology.duke.edu/nowicki/pdf/Hyman2003.pdf |url-status=live }}</ref> This implies a role in intraspecies aggressive competition towards joint resource defense.<ref>{{Cite journal |last1=Dahlin |first1=C. R. |last2=Benedict |first2=L. |date=2013 |title=Angry Birds Need Not Apply: A Perspective on the Flexible form and Multifunctionality of Avian Vocal Duets. |url=https://doi.org/10.1111/eth.12182 |journal=Ethology |volume=120 |issue=1 |pages=1–10|doi=10.1111/eth.12182 }}</ref> Duets are well known in cranes, but the Sarus Crane seems unique in infrequently also having three bonded adults defending one territory who perform "triets".<ref>{{Cite journal |last1=Roy |first1=Suhridam |last2=Kittur |first2=Swati |last3=Sundar |first3=K. S. Gopi |date=2022 |title=Sarus crane Antigone antigone trios and their triets: Discovery of a novel social unit in cranes |url=https://doi.org/10.1002/ecy.3707 |journal=Ecology |volume=103 |issue=6 |pages=e3707|doi=10.1002/ecy.3707 |pmid=35357696 |bibcode=2022Ecol..103E3707R |s2cid=247840832 |url-access=subscription }}</ref> Triets had a lower frequency relative to duets, but the functional value of this difference is not yet known.

Sometimes, songs vocalized in the post-breeding season act as a cue to [[conspecificity|conspecific]] eavesdroppers.<ref>{{cite journal |last=Betts |first=M.G. |author2=Hadley, A.S. |author3=Rodenhouse, N. |author4= Nocera, J.J. |title=Social Information Trumps Vegetation Structure in Breeding-Site Selection by a Migrant Songbird |journal=Proceedings: Biological Sciences |year=2008 |volume=275 |issue=1648 |series=1648 |pages=2257–2263 |doi=10.1098/rspb.2008.0217|pmc=2603235 |pmid=18559326}}</ref> In [[black-throated blue warbler]]s, males that have bred and reproduced successfully sing to their offspring to influence their vocal development, while males that have failed to reproduce usually abandon the nests and stay silent. The post-breeding song therefore inadvertently informs the unsuccessful males of particular habitats that have a higher likelihood of reproductive success. The [[animal communication|social communication]] by vocalization provides a shortcut to locating high quality habitats and saves the trouble of directly assessing various vegetation structures.

[[File:Grus vipio at the Bronx Zoo 006.jpg|thumb|A mated pair of [[white-naped crane]]s (''Antigone vipio'') performing a "unison call", which strengthens the [[pair bond]] and provides a territorial warning to other cranes]]
Some birds are excellent vocal [[mimicry|mimics]]. In some tropical species, mimics such as the [[drongo]]s may have a role in the formation of [[mixed-species feeding flock|mixed-species foraging flocks]].<ref>{{cite journal |author1=Goodale, E. |author2=Kotagama, S. W. |name-list-style=amp|year=2005|title=Testing the roles of species in mixed-species bird flocks of a Sri Lankan rain forest|journal=Journal of Tropical Ecology|volume=21|pages=669–676|doi=10.1017/S0266467405002609|issue=6|title-link=Sri Lanka |s2cid=86000560 }}</ref> Vocal mimicry can include conspecifics, other species or even man-made sounds. Many hypotheses have been made on the functions of vocal mimicry including suggestions that they may be involved in sexual selection by acting as an indicator of fitness, help brood parasites, or protect against predation, but strong support is lacking for any function.<ref>{{cite journal|author1=Kelley, L. A. |author2=Coe, R. L. |author3=Madden, J. R. |author4=Healy, S. D. |year=2008 |title=Vocal mimicry in songbirds |journal= Animal Behaviour |volume=76 |issue=3 |pages=521–528 |doi=10.1016/j.anbehav.2008.04.012|s2cid=53192695 }}</ref> Many birds, especially those that nest in cavities, are known to produce a snakelike hissing sound that may help deter predators at close range.<ref>{{cite book|title=Nature's music: the science of birdsong |last1=Marler|first1=Peter |first2=Hans Willem |last2=Slabbekoorn |publisher=Academic Press |year=2004 |isbn=978-0-12-473070-0 |page=145}}</ref>

Some cave-dwelling species, including the [[oilbird]]<ref>{{cite journal |name-list-style=amp|author1=Suthers RA |author2=Hector DH |year=1985|title=The physiology of vocalization by the echolocating Oilbird, ''Steatornis caripensis''|journal=J. Comp. Physiol. |volume=156 |issue=2 |pages=243–266 |doi=10.1007/BF00610867|s2cid=1279919 }}</ref> and swiftlets (''[[Collocalia]]'' and ''[[Aerodramus]]'' species),<ref>{{cite journal |name-list-style=amp|author1=Suthers RA |author2=Hector DH |year=1982|title=Mechanism for the production of echolocating clicks by the Grey Swiftlet, ''Collocalia spodiopygia''|journal= J. Comp. Physiol. A |volume=148 |issue=4 |pages=457–470 |doi=10.1007/BF00619784|s2cid=39111110 }}</ref> use audible sound (with the majority of sonic location occurring between 2 and 5&nbsp;kHz<ref>{{cite journal|name-list-style=amp|author1=Coles RB|author2=Konishi M|author3=Pettigrew JD|year=1987|title=Hearing and echolocation in the Australian Grey Swiftlet, ''Collocalia spodiopygia''|journal=J. Exp. Biol.|volume=129|issue=1 |pages=365–371|doi=10.1242/jeb.129.1.365|bibcode=1987JExpB.129..365C |url=https://authors.library.caltech.edu/32078/|access-date=2021-05-11|archive-date=2021-05-17|archive-url=https://web.archive.org/web/20210517033233/https://authors.library.caltech.edu/32078/|url-status=live|url-access=subscription}}</ref>) to [[Animal echolocation|echolocate]] in the darkness of caves. The only bird known to make use of [[infrasound]] (at about 20&nbsp;Hz) is the [[western capercaillie]].<ref>{{cite journal|title=Infrasound in the capercaillie ( ''Tetrao urogallus '' )| journal=Journal of Ornithology| volume=146|issue=4|year=2005|doi=10.1007/s10336-005-0003-y| pages=395–398 |name-list-style=amp|last1=Lieser |first1=M. |first2=P. |last2=Berthold |first3=G. A. |last3=Manley| bibcode=2005JOrni.146..395L| s2cid=22412727}}</ref>

The hearing range of birds is from below 50&nbsp;Hz ([[infrasound]]) to around 12&nbsp;kHz, with maximum sensitivity between 1 and 5&nbsp;kHz.<ref name = "Møller 2005 223-237" /><ref>{{cite book|last1=Dooling|first1=R. J.|year=1982|chapter=Auditory perception in birds|title=Acoustic Communication in Birds|volume=1|editor1-first=D. E. |editor1-last=Kroodsma|editor2-first=E. H. |editor2-last=Miller|isbn= 9780124268012|pages=95–130}}</ref> The [[black jacobin]] is exceptional in producing sounds at about 11.8&nbsp;kHz. It is not known if they can hear these sounds.<ref>{{Cite journal|last1=Olson|first1=Christopher R.|last2=Fernández-Vargas|first2=Marcela|last3=Portfors|first3=Christine V.|last4=Mello|first4=Claudio V.|title=Black Jacobin hummingbirds vocalize above the known hearing range of birds|journal=Current Biology|volume=28|issue=5|pages=R204–R205|doi=10.1016/j.cub.2018.01.041|pmid=29510104|year=2018|s2cid=3727714|doi-access=free|bibcode=2018CBio...28.R204O }}</ref>

The range of frequencies at which birds call in an environment varies with the quality of habitat and the ambient sounds. The acoustic adaptation hypothesis predicts that narrow bandwidths, low frequencies, and long elements and inter-element intervals should be found in habitats with complex vegetation structures (which would absorb and muffle sounds), while high frequencies, broad bandwidth, high-frequency modulations (trills), and short elements and inter-elements may be expected in open habitats, without obstructive vegetation.<ref>{{cite journal|last=Derryberry|first=Elizabeth|s2cid=8606774|title=Ecology Shapes Birdsong Evolution: Variation in Morphology and Habitat Explains Variation in White-Crowned Sparrow Song|journal=The American Naturalist|date=July 2009|volume=174|issue=1|pages=24–33|doi=10.1086/599298|pmid=19441960|bibcode=2009ANat..174...24D }}</ref><ref>{{cite journal |author1=Boncoraglio, G. |author2=Nicola Saino |name-list-style=amp|year=2007|title=Habitat structure and the evolution of bird song: a meta-analysis of the evidence for the acoustic adaptation hypothesis|journal= Functional Ecology|volume=21|issue=1 |pages=134–142|doi=10.1111/j.1365-2435.2006.01207.x|s2cid=86710570 |doi-access=free|bibcode=2007FuEco..21..134B }}</ref><ref>{{cite journal|author=Morton, E.S. |s2cid=55261842|year=1975|title= Ecological sources of selection on avian sounds|journal=American Naturalist|volume=109|pages=17–34|doi=10.1086/282971|issue=965|bibcode=1975ANat..109...17M }}</ref>

Low frequency songs are optimal for obstructed, densely vegetated habitats because low frequency, slowly modulated song elements are less susceptible to signal degradation by means of reverberations off of sound-reflecting vegetation. High frequency calls with rapid modulations are optimal for open habitats because they degrade less across open space.<ref>{{cite journal|last=Ey|first=Elodie|author2=Fischer, J.|title=The "acoustic adaptation hypothesis" – a review of the evidence from birds, anurans and mammals|journal=Bioacoustics|date=13 April 2012|volume=19|issue=1–2|pages=21–48|doi=10.1080/09524622.2009.9753613|s2cid=84971439}}</ref><ref>{{cite journal|last=Tubaro|first=Pablo L.|author2=Segura, Enrique T.|title=Dialect Differences in the Song of Zonotrichia capensis in the Southern Pampas: A Test of the Acoustic Adaptation Hypothesis|journal=The Condor|date=November 1994|volume=96|issue=4|pages=1084–1088|doi=10.2307/1369117|jstor=1369117}}</ref> The acoustic adaptation hypothesis also states that song characteristics may take advantage of beneficial acoustic properties of the environment. Narrow-frequency bandwidth notes are increased in volume and length by reverberations in densely vegetated habitats.<ref>{{cite journal|last=Slabbekoorn|first=Hans|author2=Ellers, Jacintha|author3=Smith, Thomas B.|title=Birdsong and sound transmission: the benefits of reverberations|journal=The Condor|year=2002|volume=104|issue=3|pages=564–573|doi=10.1650/0010-5422(2002)104[0564:basttb]2.0.co;2|s2cid=53995725|url=https://research.vu.nl/ws/files/1834141/149395.pdf|access-date=2018-11-09|archive-date=2018-07-19|archive-url=https://web.archive.org/web/20180719231815/https://research.vu.nl/ws/files/1834141/149395.pdf|url-status=live}}</ref>

It has been hypothesized that the available frequency range is partitioned, and birds call so that overlap between different species in frequency and time is reduced. This idea has been termed the "acoustic niche".<ref>{{cite journal|author=Krause, Bernard L.|year=1993|title=The Niche Hypothesis|journal=The Soundscape Newsletter|volume=06|url=http://interact.uoregon.edu/MediaLit/WFAE/library/articles/krause_niche.pdf|archive-url=https://web.archive.org/web/20080307225409/http://interact.uoregon.edu/MediaLit/WFAE/library/articles/krause_niche.pdf|url-status=dead|archive-date=2008-03-07}}</ref> Birds sing louder and at a higher pitch in urban areas, where there is ambient low-frequency noise.<ref>{{cite journal|author=Henrik Brumm|s2cid=73714706|year=2004|title= The impact of environmental noise on song amplitude in a territorial bird|journal= Journal of Animal Ecology|volume= 73|issue=3|pages= 434–440|doi=10.1111/j.0021-8790.2004.00814.x|doi-access=free|bibcode=2004JAnEc..73..434B }}</ref><ref>{{cite journal |author1=Slabbekoorn, H. |author2=Peet, M. |name-list-style=amp|year= 2003|title= Birds sing at a higher pitch in urban noise|journal=Nature|pmid=12867967|volume= 424|issue=6946|page=267|doi=10.1038/424267a |bibcode=2003Natur.424..267S|s2cid=4348883 |doi-access=free}}</ref> Traffic noise was found to decrease reproductive success in the [[great tit]] (''Parus major'') due to the overlap in acoustic frequency.<ref>{{cite journal |last=Halfwerk |first=Wouter |author2=Holleman, L.J.M. |author3=Lessells, C.M. |author4=Slabbekoorn, H. |s2cid=83619284 |title=Negative impact of traffic nosie on avian reproductive success.|journal=Journal of Applied Ecology |date=February 2011 |volume=48 |issue=1 |pages=210–219 |doi=10.1111/j.1365-2664.2010.01914.x|doi-access=free |bibcode=2011JApEc..48..210H }}</ref> During the [[COVID-19 pandemic]], reduced traffic noise led to birds in [[San Francisco]] singing 30% more softly.<ref>{{cite magazine |last=Stokstad |first=Erik |title=When COVID-19 silenced cities, birdsong recaptured its former glory |magazine=Science |date=24 September 2020 |url=https://www.science.org/content/article/when-covid-19-silenced-cities-birdsong-recaptured-its-former-glory |access-date=28 May 2021 |archive-date=23 September 2021 |archive-url=https://web.archive.org/web/20210923002204/https://www.science.org/content/article/when-covid-19-silenced-cities-birdsong-recaptured-its-former-glory |url-status=live }}</ref> An increase in song volume restored fitness to birds in urban areas, as did higher frequency songs.<ref>{{cite journal|last=Luther|first=David A. |author2=Derryberry, E.P. |title=Birdsongs keep pace with city life: changes in song over time in an urban songbird affects communication |journal=Animal Behaviour |date=April 2012 |volume=83 |issue=4 |pages=1059–1066 |doi=10.1016/j.anbehav.2012.01.034|s2cid=31212627 }}</ref>

It has been proposed that birds show latitudinal variation in song complexity; however, there is no strong evidence that song complexity increases with latitude or migratory behaviour.<ref>{{cite journal |author1= Najar, N. |author2= Benedict, L. | year=2019| title= The relationship between latitude, migration and the evolution of bird song complexity | journal=Ibis| volume=161| pages= 1–12 | doi= 10.1111/ibi.12648| issue=1| doi-access= free}}</ref>

According to a study published in 2019, the [[white bellbird]] makes the loudest call ever recorded for birds, reaching 125&nbsp;[[Decibel|dB]].<ref>{{cite journal|first1=Jeffrey |last1=Podos|first2=Mario |last2=Cohn-Haft|date=21 October 2019|title=Extremely loud mating songs at close range in white bellbirds|journal=Current Biology|volume=29|issue=20|pages=R1068–R1069|doi=10.1016/j.cub.2019.09.028|pmid=31639347|s2cid=204823663|doi-access=free|bibcode=2019CBio...29R1068P }}</ref><ref>{{cite news|url=https://www.bbc.com/news/av/newsbeat-50135578/world-s-loudest-bird-meet-the-white-bellbird|title=World's 'loudest bird': Meet the white bellbird|date=22 October 2019|publisher=BBC News|type=video|website=Newsbeat|access-date=25 October 2019|archive-date=22 October 2019|archive-url=https://web.archive.org/web/20191022195630/https://www.bbc.com/news/av/newsbeat-50135578/world-s-loudest-bird-meet-the-white-bellbird|url-status=live}}</ref> The record was previously held by the [[screaming piha]] with 116&nbsp;dB.<ref>{{cite journal|last=Nemeth|first=Erwin|date=2004-01-01|title=Measuring the Sound Pressure Level of the Song of the Screaming Piha Lipaugus Vociferans: One of the Loudest Birds in the World?|journal=Bioacoustics|volume=14|issue=3|pages=225–228|doi=10.1080/09524622.2004.9753527|bibcode=2004Bioac..14..225N |s2cid=84218370|issn=0952-4622}}</ref>

A 2023 study found a correlation between the [[Dawn chorus (birds)|dawn chorus]] of male birds and the absence of  females. The research was conducted in southern Germany, with male [[Eurasian blue tit|blue tits]] being the birds of interest. Researchers "found that the males sang at high rates while their female partners were still roosting in the nest box at dawn, and stopped singing as soon as the females left the nest box to join them". The males were also more likely to sing when the females entered the nests in the evening or even during the daytime. While this information is eye-opening, it still does not answer the question of ''why'' male birds sing more when females are absent.<ref>{{Cite news |last=Gil |first=Diego |date=February 6, 2024 |title=Absence of female partners can explain the dawn chorus of birds |url=https://www.nature.com/articles/d41586-024-00264-9 |access-date=February 7, 2024 |work=Nature}}</ref>